Question about 1996 Volvo 850

4 Answers

Just tuned up, new air filter, plugs, wires, rotor

Was and still am only getting 11 mpg. Blows grey black sooty smoke when started. After a few minutes no smoke. Raw fuel odor when stopping or shutting off the motor.

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  • bobbyrnetn Jul 14, 2010

    1996 Volvo 850 DL
    Just tuned up, new air filter, plugs, wires, rotorWas and still am only getting 11 mpg. Blows grey black sooty smoke when started. After a few minutes no smoke. Raw fuel odor when stopping or shutting off the motor.

    do u have a check engine light on?

    Jul 10, 2010 - No Check engine light is on. No codes showing. It has been tested five times in the last three days.
    Jul 10, 2010 - then it must have a powertrain control module problem, if it is runninhg as rich as u clain then it should set fault codes, what are the voltage readings from the O2 sensors? have the fuel injectors been flow tested? these are things that require a high end scan tool and a factory flow tester.

    Jul 11, 2010 - The mechanic said he tested the injectors and they are working fine. They also replaced fuel filter and fuel pressure regulator.

    He had mentioned that the spark plugs were black with carbon build up. I saw them and they looked like the build up on the tail pipe and the soot it deposits on the ground when first started up.

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  • Master
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Have your mechanic test the cars fuel pressure under normal driving conditions.

I am willing to bet that the fuel pressure is dropping and the cars computer has adjusted to compensate as best it could but its losing control of overall fuel flow. Or your fuel rail pressure regulator is stuck and the rail is overpressurizing. Either way the system cant compensate enough with injector pulse width.

You can also check to make sure the throttle position sensor isnt stuck at wide open throttle. This test would need an obd2 compatible reader that does active sampling of the input sensors while driving.


Posted on Aug 10, 2010

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  • Master
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Obviously this vehicle is running rich as heck, I need to ask was it running poorly before you tuned it? If so continue.... If it is something you disturbed I would have the wires and spark plug checked for possible damage(internal wires silicone core open, or spark plug gap smashed or insulator broken during installation) but from what you said sounds like this is a pre existing condition so..... scan the computer or have Auto zone or Discount Auto scan it for free to get an idea if there are any codes to help you find the prblem, when a vehicle is running this poor(rich, soot) I would also look to the catalyctic converter in hopes the rich mixture hasn't damaged the interior of it as yet.(excess heat from richness causes the interior honeycomb/or pellets to fuse together causing a blocked exhaust flow)
Ok what can cause a rich mixture.... bad 02 sensors giving the computer false information, hung injectors which will require either a super injector cleaning/flush or replacement, a defunct IAC Motor(Idle Air Control) which has a needle type seat device that allows the needle(Pintle) to move back and forth electronically allowing the needle to come on and off its seat(open/closed) which in turn allows more or less fuel/air mixture....these devices do go bad and can create havoc in the fuel delivery system, an open vacumn line(look for a broken vacumn line or a disconnected vac. line) this also will allow too much air into the intake manifold and demand the comuter to richen up the mixture by holding the injectors wide open... sort of like the old stuck choke syndrome back in the days of carburation. Timing may be off as well.
These are all basic, common, failures to check out, but please before you invest in anymore time and guess work have the car either scanned by a parts store(free method) or have a shop with expert scanners do the system and charge you, either way a scan must be plan #1 on your diagnostic list.
Take this first step, the soot and smoke is definately from rich unburnt fuel entering the cylinder or cylinders and getting forced out of the cylinder on the exhaust stroke, allowing this mixture to enter the catalyctic converter which now can create such a high temp that the cat will do a melt down and become clogged feeling almost like a defective fuel filter or fuel pump.
Debris in the fuel lines(dirt/scale/ rust from a gas stations under ground tanks etc.) can find itself inside a fuel injector and hold it open(off its seat) so it wont close causing a raw fuel cituation as well. If you are at the end of your rope testing to no avail.... analyse the fuel and the fuel filter using a clear and clean glass jar to see if any debris is in it.
If you find a contamination factor replace the fuel filter, drain flush the gas tank, flush the fuel lines, and have the injectors flushed by a shop that can pressure flush them...if they dont clean up you may be looking at those injectors being replaced.
I hope all this tech stuff works for you.

Posted on Aug 09, 2010

  • 1 more comment 
  • JOHN DAVIDSON Aug 09, 2010

    Hope you injested all that I wrote!!!

    Happy Diagnosing!!!!!!!!!!

  • JOHN DAVIDSON Aug 10, 2010

    Did anything I wrote have any positive affect?

  • JOHN DAVIDSON Aug 10, 2010

    I believe that you have a tank full of contaminated fuel!!!! They replaced the filter ask them why??? and regulator valve... sounds like a guess of over pressuring in the lines all that could have been sorted out by means of a fuel pressure gauge in the system, refering back to the first comment....if they tell you the filter was full of junk... then tell them to pull it once more.... if it is again full of $#@#$ then have them drop the tank drain/flush it, flush the lines, flush/test the injectors, we even had a vehicle that had a fuel tank disintegrating from the inside out, we sent the tank to get it boiled and the radiator shop cut it open and found it(when this happens through the tank away!!)

    If you find a contamination factor replace the fuel filter, drain flush the gas tank, flush the fuel lines, and have the injectors flushed by a shop that can pressure flush them...if they dont clean up you may be looking at those injectors being replaced.
    I hope all this tech stuff works for you.

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HI. Okay, The first thing i would advise to do is have a compression test ran, asap. I'm sure the rates will be below specs. The Grey smoke is a HUGE indicator of an ignition issue and head gasket problems as well. The carbon build up, if still present, will signal serious issues that concern ignition timing, air cleaner issues, ecu malfunctions etc. Here are a few more areas that i would check, asap: 1. PCV valve- The device may be clogged with carbon or damaged. Replace if needed. 2. Valve seals - This will require your mechanic to dive in a little deeper to inspect these parts. I HIGHLY recommend to replace these seals.(rebuild the entire head assembly if possible) 3. Head gasket(s) - Replace them , asap!(for 4 cyl engine , you only need one replacement gasket). This engine needs attention soon. The more you drive it with the Grey start up smoke, the more the gasket will deteriorate and threaten the entire blocks integrity.

Posted on Jul 14, 2010

  • Michael Masters
    Michael Masters Jul 14, 2010

    Additionally, check these parts as well:

    1. Coolant temperature sensor - Make sure the device isn't Disconnected or Faulty.
    2. MAP Sensor - You may have a Disconnected or Faulty MAP Sensor.
    3. Canister Purge Valve - I do suspect that this is an issue as well. The valve may be faulty or stuck closed.


    NOTE_ You should be getting countless codes, at this point, due to your symptoms and obvious compression issues. That engine computer may be malfunctioning. i would check for stored codes and burn markings on the actual CPU board. Check for water intrusion in the CPU, as well.

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Do u have a check engine light on? if so have u had the electronic engine control computer tested for fault codes? this is absolutely the 1st step to find out what the problem is, u can't just guess at this, u must have it tested and properly diagnosed to find the problem, this type of issue requires hands on, guessing will be VERY expensive and not a wise way to approch this. My experience? 35 years as a dealer tech, hold master technician certification in electronic engine control systems.

Posted on Jul 10, 2010

  • 1 more comment 
  • bobbyrnetn Jul 10, 2010

    No Check engine light is on. No codes showing. It has been tested five times in the last three days.

  • yadayada
    yadayada Jul 10, 2010

    then it must have a powertrain control module problem, if it is runninhg as rich as u clain then it should set fault codes, what are the voltage readings from the O2 sensors? have the fuel injectors been flow tested? these are things that require a high end scan tool and a factory flow tester.

  • bobbyrnetn Jul 11, 2010

    The mechanic said he tested the injectors and they are working fine. They also replaced fuel filter and fuel pressure regulator.



    He had mentioned that the spark plugs were black with carbon build up. I saw them and they looked like the build up on the tail pipe and the soot it deposits on the ground when first started up.

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